1. Field of the Invention
The present invention relates to a junction box for connecting a power supply to a load and a battery controller provided inside thereof, and more particularly to a battery controller capable of measuring a remaining capacity of each of a low voltage battery and a high voltage battery at the same time and further control timing for charging these batteries.
2. Description of the Related Art
Recently, some types of vehicles contain a high voltage battery of 36 V and a low voltage battery of 12 V. In such a vehicle, charging of the high voltage battery and low voltage battery is controlled by a battery controller provided in the junction box, which connects a vehicle power supply to its load.
The aforementioned high voltage battery is charged with 42 V by an alternator connected to an engine. Then, electric power from this high voltage is supplied to the junction box. The voltage from this high voltage battery is supplied to the load. The junction box includes a DC-DC converter for converting a voltage from the high voltage battery to a low voltage of DC14 V. This DC14 V voltage is supplied to the load and further the low voltage battery so that the low voltage battery is charged.
Generally, the junction box which connects a vehicle power supply to the load is disposed nearest the power supply. It is preferable that the remaining capacity of each of the low voltage battery and high voltage battery is obtained within this junction box.
However, the main role of a conventional battery controller provided in the junction box is to control charging of electric power to the high voltage battery and low voltage battery.
That is, the conventional battery controller has a problem that although it is disposed at a position enabling to measure the remaining capacities of both the batteries accurately, that battery controller does not measure the remaining capacity.
A method for estimation of the remaining capacity of the battery, which has been carried out at other place than the junction box conventionally is based on current accumulation method. That is, according to this method, a preliminarily charged electric amount is known and an amount of current that has already flown is subtracted from that original amount. However, this method is not capable of coping with a case where the battery is replaced during use.
Further, the conventional vehicle's remaining capacity measuring method is measurement of the remaining capacity of a single kind of the battery, and therefore, there is a problem that the conventional measuring method cannot measure the remaining capacities of plural kinds of the batteries which are often seen in recent vehicles.